Project Summary. Despite over 30 year of effort, an effective HIV-1 vaccine has yet to be developed. The envelope glycoprotein (Env) is the sole target for antibody-mediated protection from HIV infection. Animal immunizations with soluble Env trimers (SOSIPs) derived from Tier 2 viruses have induced autologous neutralizing antibodies, but failed to induce antibodies with sufficient breadth capable of neutralizing heterologous strains of HIV [1]. Monoclonal antibodies (mAbs) with the ability to neutralize a broad array of HIV strains (bnAbs) have been isolated from patients infected with HIV and these antibodies are capable of protecting against repeated viral challenge when administered by passive infusion to non-human primates (NHPs) [2, 3]. BnAbs generally arise after 2 to 3 years of infection and despite targeting a variety of epitopes on Env most share common characteristics such as high rates of somatic hypermutation (SHM) and unusually long heavy chain complementary determining region 3 (HCDR3) [4]. This project seeks to broaden autologous Tier 2 neutralizing antibodies by both increasing the level of SHM and directing SHM towards specific neutralizing epitopes. Aim 1. Broaden the specificity of vaccine elicited autologous neutralizing antibodies via iterative structure-based design of immunogens. High-resolution cryoEM structures of Env in complex with vaccine elicited antibodies will be used delineate autologous neutralizing epitopes. Structure guided redesign of neutralizing epitopes will focus on incorporating consensus amino acids in an effort induce cross-reactive antibodies. Aim 2. Increase the level of SHM by prolonging the duration of germinal center reactions using continuous antigen delivery. BnAbs develop in presence of persistent antigen that is constantly evolving. Implantable slow-release pumps will be used to mimic conditions of natural bnAb development. Aim 3. Improve trafficking of immunogens to follicular dendritic cell (FDCs). Env immunogens are poorly trafficked to FDCs due to high levels of glycosylation and poor complement fixation. Monoclonal antibodies that bind to the base of Env immunogens will be used to form in vivo immune complexes with the goal of fixing complement and improving trafficking to FDCs.